1. Field of the Invention
The present invention relates to a projection tube which is used in a projection type TV receiver, a video projector or the like.
2. Description of the Related Art
An image of a cathode ray tube can be obtained by scanning an electron beam emitted from an electron gun by means of a deflection yoke. The deflection yoke is mounted in the vicinity of a joint portion between a neck and a funnel. The deflection sensitivity is enhanced as the neck outer diameter becomes smaller. However, when the neck outer diameter is made small to enhance the deflection sensitivity, the electron gun which is accommodated in the neck portion must be miniaturized correspondingly. When the electron gun is miniaturized, the diameter of an electron lens becomes small and hence, the focusing is degraded. That is, the deflection sensitivity and the focusing performance are in an opposed relationship.
A method which can solve such a problem is, for example, proposed in U.S. Pat. No. 3,163,794. In this patent, with respect to a cathode ray tube, there is disclosed a technique which enhances the deflection sensitivity by making the outer diameter of a portion of a neck on which a deflection yoke is mounted smaller than the outer diameter of a portion of the neck in which an electron gun is accommodated. The maximum operating voltage of the cathode ray tube described in this patent is set to 16 kV.
On the other hand, with respect to a color cathode ray tube, in Japanese Laid-open Patent Publication 185660/1999, there is disclosed a technique which enhances the deflection sensitivity by making the outer diameter of a portion of a neck on which a deflection yoke is mounted smaller than of a portion of the neck in which an electron gun is accommodated.